Communicating optical signals between stacked dies

ABSTRACT

A method includes forming a stack of semiconductor die. The stack includes a first semiconductor die, a second semiconductor die and a third semiconductor die. The first semiconductor die is stacked above the second semiconductor die and the third semiconductor die is stacked above the first semiconductor die. A first optical transmitter and a first optical receiver are provided in the first semiconductor die, a second optical transmitter is provided in the second semiconductor die, and a second optical receiver is provided in the third semiconductor die. A first optical signal is transmitted from the first optical transmitter in the first semiconductor die to the second optical receiver in the third semiconductor die. A second optical signal is transmitted from the second optical transmitter in the second semiconductor die to the first optical receiver in the first semiconductor die.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Generally, the present disclosure relates to the field of manufacturingof integrated circuits and semiconductor devices, and, moreparticularly, to an integrated circuit product with die-die stackingstructures comprising connectors between individual dies and methods ofmaking such structures.

2. Description of the Related Art

The fabrication of advanced integrated circuits, such as CPUs, storagedevices, ASICs (application specific integrated circuits) and the like,requires the formation of a large number of circuit elements on a givenchip area according to a specified circuit layout. In a wide variety ofelectronic circuits, field effect transistors represent one importanttype of circuit element that substantially determines performance of theintegrated circuits. Generally, a plurality of process technologies arecurrently practiced for forming field effect transistors, wherein, formany types of complex circuitry, MOS technology is currently one of themost promising approaches due to the superior characteristics in view ofoperating speed and/or power consumption and/or cost efficiency. Duringthe fabrication of complex integrated circuits using, for instance, MOStechnology, millions of transistors, e.g., N-channel transistors and/orP-channel transistors, are formed on a substrate including a crystallinesemiconductor layer. Miniaturization and increase of circuit densitiesrepresent ongoing demands.

A conventional die (chip) is usually mounted on some form of substrate,such as a package substrate or a printed circuit board. Electricalconnectivity between the die and the underlying substrate or board isestablished through a variety of conventional mechanisms. In oneexample, a so-called flip-chip configuration, the active circuitry sideof the die is provided with a plurality of electrically conductive ballsor bumps that are designed to establish a metallurgical bond with acorresponding plurality of conductor pads positioned on the substrate orcircuit board. The die is flipped over and seated with the activecircuitry side facing downwards on the underlying substrate.

Recently, stacked die configurations have been developed in order toincrease performance and high-density integration of semiconductordevices. Electrical interconnects must be established between thestacked dies. Several conventional techniques for stacking dies havebeen considered. In one conventional variant, a relatively smallsemiconductor die is positioned on the bulk semiconductor side of a muchlarger semiconductor die. Bonding wires are used to establish theelectrical conductivity between the upper die and the lower die. Thedifficulty associated with this approach is that the bonding wiresrepresent relatively long electrical pathways and thus exhibit higherthan desired inductance and proportionally slower electricalperformance. In addition, the bulk semiconductor side is not availablefor heat sink mounting.

A so-called multi-chip module (MCM) package is commonly used in theassembly package and electronic devices. Usually, the MCM package mainlycomprises at least two chips encapsulated therein so as to upgrade theelectrical performance of the package. A first chip carrier is joined“back to back” with a second chip carrier via an insulating adhesiveapplied on the inactive surface of the first chip mounted on the firstchip carrier and the inactive surface of the second chip mounted on thesecond chip carrier. The two inactive surfaces are bonded together toform a multi-chip module. Both the topmost or upper-most surface and thelower-most surface of the multi-chip module are capable of beingelectrically connected with other components, thereby eliminating one ofthe obstacles associated with vertically stacking chips in flip-chiptechnology and further varying arrangement flexibility of the chips in apackage.

In particular, stacked dies may be electrically connected to each otherby means of through-silicon vias (TSVs) as illustrated in FIG. 1. FIG. 1shows a die 10 embedded in a substrate 11. The die 10 comprises two TSVs12 and 13. The die 10 comprises an active region 14 comprising anintegrated circuit. Die bond pads 15 are connected to the active region14 of the die 10 and to conductors 16. The conductors 16 are connectedto bump bond pads 17 in a lower layer of the substrate 11 to whichconductive bumps 18 are adhered. In the depicted prior art example, sixadditional dies 20, 30, 40, 50, 60 and 70 are stacked vertically abovethe lower most die 10 and each of the additional dies 20, 30, 40, 50, 60and 70 comprises TSVs and active portions. Electrical connectionsbetween the individual dies 10 to 70 are provided by conductive bumps19. However, as shown in FIG. 1, this design also requires a pluralityof external conductors 16 and thus exhibits relatively long electricalpathways for signal transfer.

As already mentioned, in the art, a large variety of die stackingtechniques, including a variety of electrical die-die connections, areproposed as, for example, a stack of a relatively small semiconductordie positioned on the bulk semiconductor side of a much largersemiconductor die wherein bonding wires are used to establish theelectrical conductivity between the upper die and the lower die. Thebonding wires exhibit long electrical pathways and thus a relativelyhigh inductance and low electrical performance. According to anotherapproach, electrical interconnects between upper and lower dies areprovided by a plurality of conductor traces that are formed on the bulksilicon side of the lower die. Again, the conductor traces representrelatively high inductance pathways and thus limit speed performance.Furthermore, the bulk silicon side is not available for a heat sink inthis approach.

In view of the situation described above, the present disclosureprovides techniques of die-die stacking with improved signal transferfrom die to die, in particular, with respect to enhanced signaling speedand standardization ability, as compared to the art.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order toprovide a basic understanding of some aspects of the invention. Thissummary is not an exhaustive overview of the invention. It is notintended to identify key or critical elements of the invention or todelineate the scope of the invention. Its sole purpose is to presentsome concepts in a simplified form as a prelude to the more detaileddescription that is discussed later.

Generally, the subject matter disclosed herein relates to die stackingon an integrated circuit product. According to the present disclosure, adie is provided with optical signal transmission and reception means. Inone illustrative embodiment, the individual die can communicate witheach other via optical signal transmission and reception means. Theoptical signal path allows for fast data transmission and transmissionof large data amounts in a most reliable manner. Die-to-die stackingbased on dies with optical signal transmission and reception means maybe realized in a highly standardized manner providing high data ratesand broad data bandwidths.

In one particular embodiment, a method includes, among other things,forming a stack of semiconductor die. The stack includes a firstsemiconductor die, a second semiconductor die and a third semiconductordie. The first semiconductor die is stacked above the secondsemiconductor die and the third semiconductor die is stacked above thefirst semiconductor die. A first optical transmitter and a first opticalreceiver are provided in the first semiconductor die, a second opticaltransmitter is provided in the second semiconductor die, and a secondoptical receiver is provided in the third semiconductor die. A firstoptical signal is transmitted from the first optical transmitter in thefirst semiconductor die to the second optical receiver in the thirdsemiconductor die. A second optical signal is transmitted from thesecond optical transmitter in the second semiconductor die to the firstoptical receiver in the first semiconductor die.

Another method includes, among other things, stacking a plurality ofsemiconductor die. The plurality of semiconductor die includes at leastthree semiconductor die. A first optical signal is communicated betweena second semiconductor die of the plurality of semiconductor diepositioned below a first semiconductor die and the first semiconductordie. A second optical signal is communicated between the firstsemiconductor die and a third semiconductor die of the plurality ofsemiconductor die positioned above the first semiconductor die.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure may be understood by reference to the followingdescription taken in conjunction with the accompanying drawings, inwhich like reference numerals identify like elements, and in which:

FIG. 1 illustrates die-die stacking with TSVs according to the art;

FIG. 2 illustrates a die having an optical transmitter, an opticalreceiver and TSVs;

FIG. 3 illustrates a die stack having dies with optical transmitters,optical receivers and TSVs;

FIG. 4 illustrates a top view of a die with an array of conductive bumpsand an array of optical transmitters/receivers;

FIG. 5 illustrates alignment of optical transmitters and opticalreceivers formed in semiconductor dies; and

FIG. 6 illustrates two communicating semiconductor dies, each havingoptical transmitters and optical receivers.

While the subject matter disclosed herein is susceptible to variousmodifications and alternative forms, specific embodiments thereof havebeen shown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the invention to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

Various illustrative embodiments of the invention are described below.In the interest of clarity, not all features of an actual implementationare described in this specification. It will of course be appreciatedthat in the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure.

The following embodiments are described in sufficient detail to enablethose skilled in the art to make use of the invention. It is to beunderstood that other embodiments would be evident, based on the presentdisclosure, and that system, structure, process or mechanical changesmay be made without departing from the scope of the present disclosure.In the following description, numeral-specific details are given toprovide a thorough understanding of the disclosure. However, it would beapparent that the embodiments of the disclosure may be practiced withoutthe specific details. In order to avoid obscuring the presentdisclosure, some well-known circuits, system configurations, structureconfigurations and process steps are not disclosed in detail.

The present disclosure will now be described with reference to theattached figures. Various structures, systems and devices areschematically depicted in the drawings for purposes of explanation onlyand so as to not obscure the present disclosure with details which arewell known to those skilled in the art. Nevertheless, the attacheddrawings are included to describe and explain illustrative examples ofthe present disclosure. The words and phrases used herein should beunderstood and interpreted to have a meaning consistent with theunderstanding of those words and phrases by those skilled in therelevant art. No special definition of a term or phrase, i.e., adefinition that is different from the ordinary or customary meaning asunderstood by those skilled in the art, is intended to be implied byconsistent usage of the term or phrase herein. To the extent that a termor phrase is intended to have a special meaning, i.e., a meaning otherthan that understood by skilled artisans, such a special definitionshall be expressively set forth in the specification in a definitionalmanner that directly and unequivocally provides the special definitionfor the term or phrase.

As will be readily apparent to those skilled in the art upon a completereading of the present application, the presented techniques areapplicable to a variety of technologies, for example, NMOS, PMOS, CMOS,etc., and is readily applicable to a variety of devices, including, butnot limited to, logic devices, memory devices, micro-electromechanicalsystems (MEMS), etc. Generally, manufacturing techniques andsemiconductor devices in which N-channel transistors and/or P-channeltransistors are formed are described herein. The techniques andtechnologies described herein may be utilized to fabricate MOSintegrated circuit devices, including NMOS integrated circuit devices,PMOS integrated circuit devices and CMOS integrated circuit devices. Inparticular, the processing steps described herein are utilized inconjunction with any semiconductor device fabrication process that formsgate structures for integrated circuits, including both planar andnon-planar integrated circuits. Although the term “MOS” properly refersto a device having a metal gate electrode and an oxide gate insulator,that term is used throughout to refer to any semiconductor device thatincludes a conductive gate electrode (whether metal or other conductivematerial) that is positioned over a gate insulator (whether oxide orother insulator), which, in turn, is positioned over a semiconductorsubstrate.

The present disclosure provides stacked dies that are equipped withoptical transmitters (modulators) comprising, for example, organic LEDsand optical receivers (for example, comprising photo diodes) tocommunicate which each other (hereinafter referred to generically as“OLEDS”). FIG. 2 illustrates a die 100 equipped with OLEDS 110 fortransmitting optical signals and photo diodes 120 for receiving opticalsignals. Each OLEDS 110 may comprise a light emitting layer sandwichedby (or positioned between) hole and electron transporting layers, holeand electron injecting layers and electrode layers as known in the art.Other means for transmitting and receiving optical signals may beemployed as desired. In particular, optical transceivers 115, 125including the OLEDs 110 or the photo diodes 120 and configured for bothtransmitting optical signals and receiving optical signals may beemployed.

In one illustrative embodiment, the die 100 comprises an active portion(device layer) comprising semiconductor devices as transistor devices130 formed on and partially in a semiconductor substrate 140. Individualsemiconductor devices, for example, transistors 130, are electricallyseparated from other semiconductor devices, for example, othertransistors 130, by means of shallow trench isolators (STIs) 150 formedin the semiconductor substrate 140. It is noted that the semiconductorsubstrate 140 may comprise a semiconductor layer, which in turn may becomprised of any appropriate semiconductor material, such as silicon,silicon/germanium, silicon/carbon, other II-VI or III-V semiconductorcompounds and the like. The semiconductor substrate 140 may be a siliconsubstrate, in particular, a single crystal silicon substrate. Othermaterials may be used to form the semiconductor substrate, such as, forexample, germanium, silicon germanium, gallium phosphate, galliumarsenide, etc. Furthermore, the semiconductor substrate 140 may define asilicon-on-insulator (SOI) configuration where a thin semiconductorlayer, for example, a silicon layer, is formed on a buried oxide layerthat is formed in a bulk semiconductor substrate, for example, a bulksilicon substrate.

In one illustrative embodiment, the transistors 130 may be FinFETs. Thetransistors 130 may be high-k metal gate transistor devices with gatedielectrics exhibiting a dielectric constant (“k”) larger than the oneof silicon dioxide, for example, k>5. In principle, the transistors 130may be planar or 3D transistors with a high-k/metal gate (HK/MG)structure formed according to so-called “gate last” or “replacementgate” technique or so-called “gate first” technique. In general, usingthe “gate first” technique involves forming a stack of layers ofmaterial across the substrate, wherein the stack of materials includes ahigh-k gate insulation layer, one or more metal layers, a layer ofpolysilicon and a protective cap layer, for example, silicon nitride.Thereafter, one or more etching processes are performed to pattern thestack of materials to thereby define the basic gate structures for thetransistor devices. In the replacement gate technique, a so-called“dummy” or sacrificial gate structure is initially formed and remains inplace as many process operations are performed to form the device, forexample, the formation of doped source/drain regions, performing ananneal process to repair damage to the substrate caused by the ionimplantation processes and to activate the implanted dopant materials.At some stage of the process flow, the sacrificial gate structure isremoved to define a gate cavity where the final HK/MG gate structure forthe device is formed.

As shown in FIG. 2, the photo diodes 120 are formed on or aboveinsulation regions 160. The insulation regions 160 may be formed of thesame material as the STIs 150, for example, a silicon dioxide material.The insulation regions 160 may be formed by an additional (with respectto the formation of the STIs 150) patterning sequence comprising thedeposition and patterning of a mask layer and etching of thesemiconductor substrate 140. As shown in FIG. 2, die 100 is etched onthe rear side where the semiconductor substrate 140 is provided in orderto form the insulation regions 160. Similarly, through-silicon vias(TSVs) 170 are formed by etching the rear side of the die 100 throughthe semiconductor substrate 140. The thus etched openings are filledwith an electrically conductive material in order to form the TSVs 170.The electrically conductive material may be a conductive metal or metalalloy and may comprise, for example, copper, nickel, silver, gold orplatinum. The TSVs 170 may have diameters of about 5-10 micrometers, forexample.

A number of metallization layers 180 may be comprised in the die 100.Additional active or passive semiconductor devices may be formed atdifferent levels of the metallization layers 180. The metallizationlayers 180 may be formed by plating, chemical vapor deposition, physicalvapor deposition or the like. The semiconductor devices, including thetransistors 130, photo diodes 120, OLEDS 110 and TSVs 170, areelectrically connected/contacted by conductive connectors or contacts190. In one illustrative embodiment, at the top of the die 100,conductive bumps 195 are formed for electrical contact to furtherdevices. The metallization layers 180 may comprise one or moreredistribution layers providing electrical pathways between variousconductor structures of the die 100 and the conductive bumps 195. Theconductive bumps 195 may comprise copper or aluminum, for example, andmay be formed by stencil processes or plating. In particular,connections between the conductive bumps 195 and the TSVs 170 areprovided for power routing as well as mechanical stability.

A stacked die configuration 200 according to one illustrative embodimentis illustrated in FIG. 3. A die similar to the one shown in FIG. 2represents one illustrative embodiment of a middle die 210 in FIG. 3.The stacked die configuration 200 further comprises a lower die 220 andan upper die 230. Similar to the middle die 210, the lower die 220 isequipped with optical transmitters 221, for example, in the form ofOLEDS, for signaling to the optical receivers (photo diodes) 212 of themiddle die 210. In the depicted example, optical signals areschematically illustrated by curved arrows in FIG. 3. Opticaltransmitters 211 transmit optical signals to optical receiver 232 of theupper die 230. Although not depicted in FIG. 3, the upper die 230 mayalso comprise optical transmitters and/or the lower die 220 may alsocomprise optical receivers.

In addition to optical signal connections, the stacked die configuration200 shown in FIG. 3 is equipped with electric current connections(illustrated by straight double-arrows) between the individual die 210,220 and 230 that are provided by TSVs 215 and 235 of the middle die 210and the upper die 230, respectively, and conductive bumps 217 and 227formed on the upper surface of the middle die 210 and the lower die 220,respectively.

It should be noted that integrated cooling systems, for example, airgaps, water cooling, liquid nitrogen cooling, etc., may be provided inthe stacked die configuration 200 shown in FIG. 3 as well as theindividual die 100 as shown in FIG. 2. For example, a heat sink can beadhered or thermally connected to the substrate of a die, for example,the bottom part of the semiconductor substrate 140 of the die 100 shownin FIG. 2.

As already described above, in one illustrative embodiment, a diemanufactured in accordance with an embodiment disclosed herein maycomprise TSVs and bumps for electrical connections between individualdies and optical connections provided by optical transmitters andreceivers. For example, as illustrated in FIG. 4, a die 300 may comprisea central optical array 310 built by optical transmitters/receivers foroptical signaling and a bump array 320 framing the optical array 310 forelectric current signaling.

In one illustrative embodiment, a die according to an embodiment maycomprise a modulation circuitry provided in order to enhance the signalstrengths of the optical signaling. Moreover, optical signaling may beimproved by accurate alignment of optical transmitters and opticalreceivers of individual stacked dies.

FIG. 5 is one illustrative embodiment that shows a top view of anillustrative die 400 wherein macroscopic handshake alignment of opticaltransmitters 410 and optical receivers 420 may be performed. During thehandshake alignment, it may be particularly determined which opticalreceivers 420 detect signals transmitted by which particular opticaltransmitters 410. In one illustrative example, alignment of opticaltransmitters and optical receivers of individual stacked dies may beperformed physically based on conductive TSVs bumps. Subsequently, theplurality of die may be encapsulated and accurate alignment may be doneon a software basis or by a suitably configured circuitry based on ahandshake mechanism. For example, each of the optical transmitters 410may transmit regular signals, for example, various regular checkerboardsincluding irregular patterns, and an appropriate circuitry evaluates thesignals received via some detector grid. Optical transmitters 410 andoptical receivers 420 may be assigned to each other based on thedetermined best signal-response characteristics.

As illustrated in the bottom portion of FIG. 5, signal strengths may beoptimized by assigning more than one optical transmitter to an opticalreceiver and using interference effects. A modulation circuitry 430 maybe connected to individual optical transmitters 410 of an array ofoptical transmitters 410, and a detection circuitry 440 may be connectedto a particular optical receiver 420 assigned for the detection ofoptical signals emitted from the array of optical transmitters 410. Themodulation circuitry 430 may be configured to modulate the strengths ofthe individual signals transmitted by the optical transmitters 410and/or the strength of a combined optical signal generated by thecombined optical signals transmitted by the optical transmitters 410.Particularly, the modulation circuitry 430 may have multiplexingcapabilities.

FIG. 6 illustrates a first semiconductor die 600 with an opticaltransmitter 605 and an optical receiver 610 and a second semiconductordie 615 with an optical transmitter 620 and an optical receiver 625. Theoptical transmitter 605 transmits an optical signal to the opticalreceiver 625 of the second semiconductor die 615 and the opticalreceiver 610 receives an optical signal from the optical transmitter 620of the second semiconductor die 615. The optical transmitter 605 and theoptical receiver 610 may be part of a combined optical transceiver 630,and the optical transmitter 620 and the optical receiver 625 may be partof a combined optical transceiver 635.

As a result, a novel semiconductor device is provided comprising aplurality of stacked die that are equipped with optical transmitters andreceivers. Signaling via the optical transmitters and receivers may beperformed by one die to one or more other ones of the stacked dies.Reliable and fast communication of large amounts of data may thereby berealized. Moreover, the optical signaling does not result in undesiredparasitic capacitances. In particular, the technique comprising theoptical transmitters and receivers may be readily integrated with thetechniques of signaling by means of electrical currents flowing throughTSVs. The provided techniques may, in particular, be integrated in 14,10 or 7 nm VLSI CMOS technologies.

The particular embodiments disclosed above are illustrative only, as theinvention may be modified and practiced in different but equivalentmanners apparent to those skilled in the art having the benefit of theteachings herein. For example, the process steps set forth above may beperformed in a different order. Furthermore, no limitations are intendedto the details of construction or design herein shown, other than asdescribed in the claims below. It is therefore evident that theparticular embodiments disclosed above may be altered or modified andall such variations are considered within the scope and spirit of theinvention. Note that the use of terms, such as “first,” “second,”“third” or “fourth” to describe various processes or structures in thisspecification and in the attached claims is only used as a shorthandreference to such steps/structures and does not necessarily imply thatsuch steps/structures are performed/formed in that ordered sequence. Ofcourse, depending upon the exact claim language, an ordered sequence ofsuch processes may or may not be required. Accordingly, the protectionsought herein is as set forth in the claims below.

What is claimed:
 1. A method, comprising: forming a stack of semiconductor dies, said stack comprising a first semiconductor die, a second semiconductor die and a third semiconductor die, wherein said first semiconductor die is stacked above said second semiconductor die and said third semiconductor die is stacked above said first semiconductor die; providing a first optical transmitter and a first optical receiver positioned in said first semiconductor die, a second optical transmitter in said second semiconductor die, and a second optical receiver in said third semiconductor die; transmitting a first optical signal from said first optical transmitter in said first semiconductor die to said second optical receiver in said third semiconductor die; and transmitting a second optical signal from said second optical transmitter in said second semiconductor die to said first optical receiver in said first semiconductor die.
 2. The method of claim 1, wherein said first semiconductor die further comprises at least one through-silicon via, and the method further comprises electrically connecting said first semiconductor die to at least one of said second semiconductor die and said third semiconductor die using said at least one through-silicon via.
 3. The method of claim 1, wherein said second semiconductor die further comprises a plurality of conductive bumps formed on an upper surface thereof, said first semiconductor die comprises a semiconductor substrate and a plurality of through-silicon vias formed at least partly in said semiconductor substrate, and the method further comprises interfacing said plurality of through-silicon vias with said plurality of conductive bumps to electrically connect said second semiconductor die to said first semiconductor die.
 4. The method of claim 1, wherein said first semiconductor die comprises a plurality of optical transmitters including said first optical transmitter, and the method further comprises modulating at least one of the strengths of optical signals transmitted by said plurality of said optical transmitters and the strength of an optical signal resulting from a combination of optical signals transmitted by said plurality of said optical transmitters.
 5. The method of claim 1, wherein at least one of said first and second optical transmitters has one of an LCD, an LED and an organic LED and at least one of said first and second optical receivers has a photo diode.
 6. The method of claim 1, wherein providing said first optical transmitter and said first optical receiver comprises providing a first optical transceiver comprising said first optical transmitter and said first optical receiver.
 7. The method of claim 1, wherein providing said second optical transmitter comprises providing an optical transceiver comprising said second optical transmitter.
 8. The method of claim 1, wherein providing said second optical receiver comprises providing an optical transceiver comprising said second optical receiver.
 9. A method, comprising: stacking a plurality of semiconductor dies, wherein said plurality of semiconductor dies includes a first semiconductor die, a second semiconductor die positioned below said first semiconductor die, and a third semiconductor die positioned above said first semiconductor die, wherein said first semiconductor die comprises a plurality of optical transmitters; communicating a first optical signal between said first semiconductor die and said second semiconductor die; communicating a second optical signal between said first semiconductor die and said third semiconductor die; and modulating at least one of the strengths of optical signals transmitted by said plurality of said optical transmitters and the strength of an optical signal resulting from a combination of optical signals transmitted by said plurality of said optical transmitters.
 10. The method of claim 9, wherein said second semiconductor die further comprises a plurality of conductive bumps formed on an upper surface thereof, said first semiconductor die comprises a semiconductor substrate and a plurality of through-silicon vias formed at least partly in said semiconductor substrate, and the method further comprises interfacing said plurality of through-silicon vias with said plurality of conductive bumps to electrically connect said second semiconductor die to said first semiconductor die.
 11. The method of claim 9, further comprising: providing a first optical transmitter of said plurality of optical transmitters and a first optical receiver positioned in said first semiconductor die, a second optical transmitter in said second semiconductor die, and a second optical receiver in said third semiconductor die; transmitting a first optical signal from said first optical transmitter in said first semiconductor die to said second optical receiver in said third semiconductor die; and transmitting a second optical signal from said second optical transmitter in said second semiconductor die to said first optical receiver in said first semiconductor die.
 12. The method of claim 11, wherein at least one of said first and second optical transmitters has one of an LCD, an LED and an organic LED and at least one of said first and second optical receivers has a photo diode.
 13. The method of claim 11, wherein providing said first optical transmitter and said first optical receiver comprises providing a first optical transceiver comprising said first optical transmitter and said first optical receiver.
 14. The method of claim 11, wherein providing said second optical transmitter comprises providing an optical transceiver comprising said second optical transmitter.
 15. The method of claim 11, wherein providing said second optical receiver comprises providing an optical transceiver comprising said second optical receiver. 